The present invention relates to a coated substrate.
The ink jet method of printing is a rapidly growing, commercially important printing process because of its ability to produce economical, high quality, multi-colored prints. Ink jet printing is becoming the method of choice for producing colored hard copy of computer generated images consisting of graphics and fonts in both narrow and wide format.
In general, the ink used in ink jet printing consists of an aqueous solution of dye, a humectant, and a pH buffer. These formulations are desirable because of their low cost, availability, safety, and environmental friendliness. In ink jet printing uniformly shaped droplets of the aqueous formulation are ejected from a nozzle as very small drops onto a printing substrate. The printing substrate should allow for printing of round, well-shaped dots of high optical density. The substrate should control feathering (spreading) of the ink drops and absorb the ink vehicle rapidly (fast dry time) while adsorbing the dye at the surface to give sharp high density prints. Ideally, the substrate should also "fix" the dyes (i.e., cause them to become water insoluble), so as to cause the print to be moisture and water resistant. Practically, however, it is very difficult to obtain all the above properties in one ink jet printing substrate.
There are a large number of references which relate to ink jet printable substrates. The typical substrate is a paper or other material having an ink-receptive coating. The coating typically includes one or more pigments and a binder. Pigments which have been used, alone or in combination, include, by way of illustration only, silica; clay; calcium carbonate; talc; barium sulfate; diatomaceous earth; titanium dioxide; cation-modified non-spherical colloidal silica, in which the modifying agent is aluminum oxide, hydrous zirconium oxide, or hydrous tin oxide; calcium carbonate-compounded silica; prismatic orthorhombic aragonite calcium carbonate; alumina; aluminum silicate; calcium silicate; kaolin; magnesium silicate; magnesium oxalate; magnesium-calcium carbonate; magnesium oxide; magnesium hydroxide; high-swelling montmorillonite clay; amorphous silica particles having a coating of a Group II metal; synthetic silica; and micro-powder silica. In some instances, the pigment may have certain defined requirements, such as particle diameter, oil absorption, surface area, water absorption, refractive index, and solubility in water.
Various binders have been employed to form the ink-receptive coating. Examples of such binders include, again by way of illustration only, a mixture of esterified starch and a water-insoluble cationic polymer; an epoxy resin and a thermoplastic resin; acrylic resins and other water-soluble polymers; a mixture of an alkylquaternaryammonium (meth)acrylate polymer and an alkylquaternaryammonium (meth)acrylamide polymer; poly(vinyl alcohol); a mixture of an acrylic resin and poly(vinyl alcohol); polyvinylpyrrolidone or vinylpyrrolidone-vinyl acetate copolymer or mixture thereof; an amine salt of a carboxylated acrylic resin; oxidized or esterified starch; derivatized cellulose; casein; gelatin; soybean protein; styrene-maleic anhydride resin or derivative thereof; styrene-butadiene latex; and poly(vinyl acetate).
Additional materials have been included in the ink-receptive layer, such as a cationic polymer. Moreover, two or more layers have been employed to form the ink-receptive coating.
In spite of the large number of improvements to ink jet printing substrates, there still is not a single substrate which satisfactorily produces sharp prints of brilliant color without feathering and which will not bleed when exposed to moisture or water. Thus, there is an opportunity for an improved substrate for ink jet printing which has been developed specifically to overcome the foregoing disadvantages.